To meet the demand for ever-increasing wireless data traffic since commercialization of the 4th generation (4G) communication system, there have been efforts to develop an advanced 5th generation (5G) or pre-5G communication system. The 5G or pre-5G communication system is called a beyond 4G network communication system or post LTE system.
Implementation of the 5G communication system using ultra-frequency (mmWave) bands, e.g., 60 GHz bands is considered to achieve higher data rates. To reduce propagation loss of radio waves and increase a transmission distance in the ultra-frequency bands, beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beamforming, large-scale antenna techniques are under discussion.
To improve system networks, technologies for advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device to device (D2D) communication, wireless backhaul, moving networks, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation and the like are also being developed in the 5G communication system.
In addition, in the 5G system, an advanced coding modulation (ACM), e.g., hybrid frequency-shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM), sliding window superposition coding (SWSC), and an advanced access technology, e.g., filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), sparse code multiple access (SCMA) are being developed.
In the meantime, as the Internet of things (IoT) emerges, interest is rising in a D2D communication technology as a communication method for working with smart devices. The D2D communication technology is operated based on physical proximity between devices, and has a lot of benefits in terms of increased efficiency of a network resource, decreased power consumption of a device, expanded cellular communication range, etc. In order to reflect these situations, the D2D technology was selected in 3GPP Release 12 as a study item as of 2011, followed by the start of a study on its validity in the name of proximity-based service (ProSe), and real standardization work has been proceeded from 2013.
During the D2D communication, a D2D user equipment (UE), which is a transmitter, can transmit data packets to a UE group including intended D2D UEs or broadcast data packets to all the D2D UEs. D2D communication between the transmitter and receiver(s) is inherently connectionless. In other words, there is no connection set up between the transmitter and the receiver until the transmitter starts to send data packets. Furthermore, in sending the data packets, the transmitter includes source identification (ID) and a destination ID in the data packet. The source ID is set to the UE ID of the transmitter. The destination ID is a broadcast ID or group ID of an intended receiver of the packet for transmission.
One of the D2D communication requirements is to enable a remote UE out of coverage of a network to communicate with the network via another UE, which is in coverage of the network and is in proximity to the remote UE. Such a UE serving as a relay is termed as a ‘UE-to-network relay’.
FIG. 1 shows communication between a remote UE and a UE-to-network relay using D2D communication according to the related art.
Referring to FIG. 1, a remote UE 101 is a UE, which may communicate with a network through a UE-to-network relay 102 and is in coverage of the network while trying to communicate with the network through the UE-to-network relay. D2D communication 104 is performed between the remote UE 101 and the UE-to-network relay 102, and cellular communication 105 is performed between the UE-to-network relay 102 and an evolved node B (eNB) 103.
A D2D direct discovery process is used to discover a UE-to-Network relay. In order for the remote UE 101 to discover the UE-to-network relay 102, the UE-to-network relay 102 may periodically send (or announce) discovery information (e.g., its UE ID and indication that it is a UE-to-network relay) in a relay discovery announcement message. The remote UE may use the relay discovery announcement message in searching/discovering a nearby UE-to-network relay. The remote UE monitors discovery resources or physical channels for discovery information sent by nearby UEs to discover a UE-to-network relay in its proximity. Furthermore, the remote UE may search/discover a UE-to-network relay by sending a discovery solicitation message indicating that it is searching/discovering a UE-to-network relay. The UE-to-network relay involved in relaying monitors the discovery resources or physical channels for the relay discovery solicitation message from the remote UE, and responds to the relay discovery solicitation message with a relay discovery announcement message or a response message.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.